The present invention relates to a device and a method for reading color images by resolving three colors of RGB into a R light, a G light and a B light.
In a color scanner, a light source irradiates a light to a manuscript and a charge is accumulated in a Charge Coupled device (referred to as CCD hereinafter) by the light reflected from the manuscript.
Then, the charge is read as a color image. The volume of accumulated charge is small compared with the volume of the light received from the manuscript when the CCD is used. Namely, a device for reading color images whose sensitivity of the CCD was improved has been adopted, since the sensitivity of the CCD was deteriorated.
The device for reading color images reads a color image by resolving three colors of R (red), G (green) and B (blue) reflected from the manuscript into each color, when the light source irradiates the manuscript. Up to the present, the following methods of every kind have existed as methods for resolving the RGB.
For instance, the device for reading color images shown in FIG. 17 comprises a R light source 31R having a wavelength of R light, a G light source 31G having a wavelength of G light and a B light source 31B having a wavelength of B light. The light of each light source reflected from the manuscript 18 is inputted into CCD 35 through a lens 34 in order, when the R light source 31R, the G light source 31G and the B light source 31 B are switched on in order.
Then, a color image (a color signal) consisting of a R signal, a G signal and a B signal is obtained from the CCD 35.
In addition, a device for reading color images shown in FIG. 18 includes a daylight fluorescent lamp 11 having a wavelength of RGB light. In the device for reading color images, an optical resolution filter 33 for the R light, the G light and the B light is installed between the lens 34 and the CCD 35. The optical resolution filter 33 is moved synchronizing it with the reading of the color image.
Hereupon, an optical resolution filter 33R resolves the R light from the RGB light radiated from the daylight fluorescent lamp 11, when the optical resolution filter 33R is arranged on an optical path. An optical resolution filter 33G resolves the G light from the RGB light beamed from the daylight fluorescent lamp 11, when the optical resolution filter 33G is arranged on the optical path.
An optical resolution filter 33B resolves the B light from the RGB light beamed from the daylight fluorescent lamp 11, when the optical resolution filter 33B is arranged on the optical path. A color image consisting of a R signal, a G signal and a B signal is obtained from the CCD 35.
Further, the device for reading color images shown in FIG. 19 comprises a daylight fluorescent lamp 11 CCD 35R, a CCD 35G and a CCD 35B for the RGB, and a R resolution reflection filter 37R, a G resolution reflection filter 37G and a B resolution reflection filter 37B corresponding to the CCDs. The resolution reflection filters reflect only specific wavelengths and are called a dichroic mirror.
As shown in FIG. 20A, the B resolution reflection filter 37B permeates the G light and the R light of the RGB light beamed from the lens 34, and reflects only the B light to transmit the reflected B light to the CCD 35B.
As shown in FIG. 20B, the G resolution reflection filter 37G permeates the B light and the R light of the RGB light beamed from the lens 34, and reflects only the G light to transmit the reflected G light to the CCD 35G.
As shown in FIG. 20C, the R resolution reflection filter 37R permeates the B light and the G light of the RGB light beamed from the lens 34, and reflects only the R light to transmit the reflected R light to the CCD 35R. As mentioned hereinbefore, the color image consisting of the R signal, the G signal and the B signal can be obtained by using the three CCDs.
However, a device for reading color images shown in FIG. 17 needs three light sources for the RGB. Accordingly, the device is high-priced and will be oversized. Besides, in a line-sequential scanning method suitable for image processing for obtaining a color image of the RGB per line, it is necessary to switch on the light source at a high speed. However, it was difficult to read the color image at a high speed, since the activation is slowed down due to the afterglow of the light source.
Further, a device for reading color images shown in FIG. 18 needs such moving parts as a motor which moves the optical resolution filter. Besides, in the line-sequential scanning method, it was necessary to move the optical resolution filter at a high speed synchronizing it with the reading of the color image.
Further, a device for reading color images shown in FIG. 19 needs three CCDs. Accordingly, the device will be oversized and will be high-priced. In this case, three more optical paths are needed, and the construction will be more complicated.